Opposed free piston reciprocating gas compressor



June 23, 1959 G. v. B. HALL ET AL 2,891,718

OPPOSED FREE PISTON RECIPROCATING GAS COMPRESSOR Filed Nov. e, 195s nited State oPPosED rmEEPrs'roN resonatecATiNG` GAS COMPRESSOR Y George V. B. Hall, Euclid, Ohio, Achilles C. Sampietro, Detroit, lvlich., and Albert K. Hannum, Willowick, Ohio, assig'nors to Thompson Ramo Wooldridge inc.,

The present invention relates to improvements in gas compressors and` more specically to a hydraulically operated free piston reciprocating gas compressor. The present invention contemplates the provision of a cylindrical compression chamber containing a pair of opposed free operating compression pistons forced together in a compression stroke by working pressurized hydraulic fiuid and forced apart in the return stroke by a compression spring. The pistons are provided with aninternal coaxially bored compressed gas delivery passageway terminating in a cylindrical coaxial extension on the outer end of each of they pistons with the extension projecting slidably into ya coaxial compression chamber extension communicating with a gas delivery conduit provided with a non-return valve.

Automatic reciprocation ofthe free opposed pistons is obtained by self-actuation with the ilow of pressurized actuatingfluidvcontrolled by a spool valvemovable in a valve chamber toV alternately communicate the ends of the compression chamber with the compressed'working fluid and with the reservoir.v The valve' spoolrecip'rocate's within the valve chamber by action of thel compressed working fluid which is conducted to the valve chamber through rst, second` and third Valve operating ports" that are placed in` communication by being exposed by movement of the first piston and by being aligned with yalvalve operating passageway'ithroughf the second piston. Thel valve' spool is moved to its return position byan operating spring and by 'being vented through first, second', 'third'and *fourth` valve operating ports and rst and second valve relieving pa'ssageways to vent the valve to the reservoir. v

It is accordingly an' objective of the present invention to provide an' improved, opposed freepiston gas'compressor operated'by pressurized hydraulic' Huid, constructed, operated an'd 'controlled iny the manner above described. i

Aw broader aspect of the invention is to provide a gas compressor whili'willeliminate oscillatory vibration by utilizing, Oippsed Simultanes Operating free Pistons.

Another'object oftheinvention is'tto provide anv irnproved'ga's compressor utilizing "opposed free pistons which are internally ported, and connected for self-actuated reversal of the pistonstroke.`

'Anotherl object of'the'invention is to provide an improved g'as compressory utilizing` opposed freeV pistons, whichf 'is adaptable to either a single'stage or,` to a' two stagegas compressor.

Another object of theV invention istoprovide an oppossd`ftee piston hydraulically Operated sas 'compressolf'wherein fiillcompiession 'strokes of the 'opposed p istQnSfare assured. i' n object of ,je invention is to provide a hydraulically operated' 'gas o m re "whieh employs' afre'oiprocating #theme01'fthsbisfen iethrlsuhsslto ain'etl'` aj simplified controlvalve opthvll r raulic uidffr actuating the 'compresi "arent Other objects and advantages will becomev more apparent from the teaching of the priciples'ofthe invention'in the disclosure of the preferred embodiments thereof in the specification and drawings, in which:

'Figure 1 is a vertical sectional vie'w partially in diagrammatic form illustrating the construction of the compressor and the control valve; and` Figure 2 is another View of thel compressor and control valve similar to Figure 1, but with the opposed pistons in their closed discharge position and the control valve moved to a positiony to permit the pistons to return in their intake stroke.

While the features ofthe invention are best disclosed with. the description of the preferred embodiment'described 'and shown herein, it will be understood that the various' elements, and features 'of the invention, while iinding particular utility inthe combination shown, may be utilizedv and. their adyantages exploited in other arrangements, as willbe recognized by those skilled in the art. Y

As illustratedin Figures 1 and 2, the compressor includes a chamberl 4, which is preferably cylindrical in shape so as to contain a pair of opposed free cylindrical compressing pistons' 6 and 18. The pistons arev shown at the end of their intake stroke in Figure l after having drawn a gas suchfas air into the chamber 4 in the space 10 between themkand shown in Figure 2` as they appear at the end of' theirrst stage compression stroke.

The cylindrical chamber 4 is formed of a cylindrical wall 12 havingv end Walls 14 and 16. At each' end of thev chamber 4, projectingV outwardly coaxially from the chamber are a firstl and second compression chamber extension 18 and 2t), each of which, is of smaller diameter than the main chamber.' The pistons 6 and 8 each have a piston extension 22 and 24, which are slidably engaged in the cylinder extensions 18 and 20.

The hollow ends of the compression chamber extensions 18 and 20 communicate with compressed gas de'- livery conduits 2 6- andv 2,8. Each of these `conduits is provided with4 a non-return valve 30 and 32, which are of the conventional'jtypeof check valve havinga spring loadedwball whichrseats to( prevent the return of gas, but Iwhich is unseated by the delivery of a flow of gas of higher pressure than the downstream pressure in the conduit. 4

When the iirst and seondv pistons 6` and 8 move togetherA to compress-the gas in the volume 10, the gas is forced out through the gas delivery passageways 34 and 36 extending in the form lofycoaxial bores through the center ofV each of the pistonsrand terminating in the piston extensions 22 and 24,. Each of the gas delivery passageways'jis also provided with a non-return valve 38 and 40, lwhichis in the form of a spring compressed ball check valve similar to that shown in the gas delivery conduit at 30 and 32. These check valves will permit the passage of gas when the pistons are moved toward each other to reduce the size of the chamber 10 between them.

Although the sizeof the chambers 42 and 44 at the end of the piston extensions within the cylinder extensions becomes larger, the diameters o f these chambers are so much smaller than the diameter of the chamber 4 that the total'available volume for the gas will be re* duced and the compressed' gas *will be forced equally out through the two gas delivery conduits 26 and 28. When the pistons 6l and 8 again separate or moveapart in their intake stroke, the chambers 42 and 44 ofthe compression` chamber extensionis18 and 20 will be reduced in' volume, and the'check valves 38 and 40 will preventfthe'"escapefgas thereby causing a secondary delivery ofcompr'essefd gasv out through 'the conduits 2,6 and28. Y" I" anemia The cornpression pistons 6 and 8 are forced apart in their intake stroke by a spirally shaped coil compression spring 44. The spiral shape of this spring permits it to be condensed to a fully compacted spiral when the pistons are together as is illustrated in Figure 2.

When the pistons move apart in their intake stroke, gas is drawn in through the air or gas intake conduit 46. This intake conduit is provided with a non-return valve 48, which is in the form of a spring loaded ball check valve, and the check valve will seat to prevent the escape of air or gas within the chamber l when the pistons f5 and 8 move together in their discharge stroke.

The motive power for operating the pistons is obtained from a pressurized duid, such as a hydraulic uid in the form of oil or the like. While not being restricted to operation by one type of liuid, for convenience of description the material will be interchangeably referred to as oil or hydraulic or operating fluid. Operating uid is admitted from a fluid or oil pump delivering into the conduit 59. The fluid passes through the control valve i, which is operated in a manner to be later described, and splits to the duid operating conduits 52 and 54 leading to thc rst and second ends of the compression chamber 4. The conduits 52 and S4, leading to the ends of the chamber i become return conduits to permit the breakdown of pressure at the ends of the pistons 6 and 3, and to permit the return of fluid to the reservoir through the conduit 56 when the pistons are moved to their return position, as illustrated in Figure l.

The conduits 52 and 54 connect to the control valve 5l through the base of the T-connection 58.

The control valve comprises a control valve chamber 66, which is preferably cylindrical in form and which contains the valve spool 62. The valve spool 62 is shown at the right end of the chamber 68 in Figure l, wherein the right end 64 of the valve chamber is relieved, and the spool is shown in its left position in the valve chamber in Figure 2 wherein the spool is actuated by uid pressure in the end 64 of the valve chamber.

The valve spool 62 is urged to its relieved position, in Figure l, by the spool operating spring 66 which is compressed between the left hand end of the spool 62 and the base 68 of the valve chamber. A boss 70 may be provided in the chamber for holding the spring and to serve as a stop to limit the motion of spool 62 (Fig. 2). The dead volume at the left end of the chamber 66 is suitably vented at 7l either directly to the atmosphere or to the reservoir.

When in the relieved position, as shown in Figure l, the valve spool 62 permits communication between the duid pressure conduit 50 and the conduits 52 and 54 leading to the compression chamber 4. This fluid communication is possible through a passageway 72 in the spool shown in the form of an annular groove extending cornpletely around the spool. At the ends of the annular groove the full diameter of the valve spool forms a land 74 to prevent the oil from leaking into the compartment housing the spring 66, and another land 76 to direct the flow of the pressurized fluid up into the conduit SS.

When the valve spool is in its operated position, as shown in Figure 2, communication is permitted between the passageway 56 leading to the reservoir, and the passageways 52 and 54 leading to the ends of the compression chamber 4. This communication is afforded by the valve by the passageway 7S shown in the form of an annular groove around the valve spool leaving the full diameter land 80 on the spool to isolate the fluid in the end 64 of the valve chamber 6i) from the iluid in cornrnunication with the reservoir conduit 56.

When the valve spool 62 is in the position of Figure l, the pistons 6 and 3 will move together in the directions indicated by the arrows 82 and 84. As the pistons move together they reach the closed compressed position of Figure 2, and at this point the valve spool 62 is moved to the position of Figure 2. To cause the valve spool 62 to move from the relief position of Figure l to the operated position of Figure 2, pressurized operating iluid from the left end 86 of the compression chamber is permitted to ow down into the end 64 of the charnber 60. The fluid flows through the first valve operating port 88, which is uncovered by the rear end 90 of the piston 6. The operating iluid then iiows through a connecting passageway 92 to the second valve operating port 94 which also extends through the cylindrical wall i2 of the compression chamber. At this point the port dat is aligned with the valve operating passageway 96 that extends through the second piston 8, and which is shown in the form of an annular groove extending around the piston. This passageway 96 communicates with a third valve operating port 98 that connects to the valve operating conduit i6@ to feed pressurized fluid down into the end 64 of the chamber to act against the end of the valve spool 62 forcing it against the action of its spring 66 and moving it to the position shown in Figure 2. This causes the reservoir conduit 56 to be placed in communication with the conduits 52 and 54 leading to the ends of the compression chamber 4. The pressure of the compressed Huid therein will then break down and the fluid will begin to ow back to the reservoir whereupon the coil compression spring 44 will spread the pistons 6 and 8 causing `an intake of air or gas through the intake 46 and also forcing the smaller remaining portion of compressed air or gas out of the chambers 42 and 44. When the pistons have been pushed back to the end of their intake stroke, moving in the direction of the arrows 102 and 104, as shown in Figure 2, the valve spool 62 is automatically returned to its relieved position of Figure 1.

When the second piston 8 reaches its return position, its valve relieving passageway 106 will permit communication between the valve operating ports 94 and 98. The valve relieving passageway 106 is shown in the form of an annular groove. This permits escape of the oil or actuating uid from the valve chamber up through the conduit MNB to pass through conduit 92, through the valve operating port 8S and through the second valve relieving passageway 10S, which extends through the rst piston 6. This second valve relieving passageway T88 is shown in the form of an annular groove around the piston. The passageway 108 permits communication between the valve operating port 88 and the valve relieving port 110. This port extends through the wall l2 of the compression chamber 4 and connects to a conduit M2 connecting to the reservoir conduit S6. This permits the actuating uid to flow back to the reservoir and the valvc spool 62 will return to the relieved position whereupon the actuating duid from the oil pump will again be com municated to the ends of the compression chamber 4.

It will be noted that the rst piston 6 is provided with an additional unusable annular groove 118, this groove making the piston 6 identical to the piston 3 for ease of manufacture and interchangeability in assembly or repair.

Although the operation of the compressor and control valve will be clear from the description of the individual elements and their relationship to the entity as a whole, a review of the description will be helpful in understanding the operation and appreciating the objectives and advantages of the invention.

With the valve spool 62 shown in the relieved position in Figure l, pressurized operating uid is fed through the conduit S0, through the passageway 72 past the valve spool, through passageway 58 and to the passageways 52 and 54 leading to the ends of the compression chamber 4. This forces the pistons 6 and 8 toward each other reducing the area of the chamber l@ between them and forcing the gas out through the passageways 34 and 36 through the center of the pistons. The gas will leave the compressor through the delivery conduits 26 and 26.

essaim.

Wherrthe pistonsA reach the, full. extentV of.v their` compressed. travel, andonly when both pistons. are completely to the center of the chamber 4, thevalve spool' 62Will change from..the. relieved lto the operated position of Figure.2.. It. is. to be noted` thatstopmembers 116.'are provided inthechamber 4. betweenthe. pistons. sothat ifv one piston, reaches the center ofthe chamber first,y it will be stopped. until the other. pistonreachesthe center. At. this point the rear face 90V of the rst piston`6 uncovers the rst `valve operatingport .88, permitting. pressurized fluid toilow. throughthe` passageway 92, andV through the secondvalve operating port 94. The fluid uthen -iiows through the annular passageway 96VA around the secondv piston. .8, through the. third valveoperating` port 98',.dow'n through the .conduitu..100and to the end 64offthe valvechamber 6i)- This .forces thevalve spool 62 to the left to cause a communicationbetween the conduits 52 and 54 and the reservoir conduit 56, which permits 'the fluid to drain from the ends ofthe compression chamber 'back tothe reservoir. The spring, 44. between the pistons Gand-8 returns the, pistonin their intake. stroke and air willl be. drawninthroughthe intake conduit 46. This also, forces thecompressed. air out ofthe chambers 42 and 44 with` the escape of air back through the pistons being preventedv by the check valves 38 and 40.

When the pistons 6 and 8 reach their return position, iiuid escapes from the valve chamber 60 up through conduit 100, valve operating portv 98, valve relieving passageway 162, Valve operating port 94, passageway 92, valve operatingport 88, valve relieving passageway 108, and valve relieving port 110. The fluid flows down through the conduit 112 and. back. to the reservoirr conduit 56 thusy permitting the valve spool 62to move to its ,relieved position whereupon the cycle of operation ofthe compresser is. again. repeated.,

Thus it will be. seen, that we have provided anopposedfree'piston compressorV which meets the objectives and advantages hereinfbefore set forth. The pistons operate simultaneously and eliminate the usual oscillatory vibrationV that accompanies the operation of a compressor. The pistons are internallyk portedv and, therefore, selfactuated for automatic reversall'of. the pistonl stroke. A full stroke of both pistons is insured since the operating valvewill not change positions until both pistons are properly yat the. end ofY their stroke.

As will be apparent to .those skilled in the art, in certain circumstances it maybe desirable to use only a single piston instead. of. the two opposed pistons. This, ofcourse, couldbe accomplished by providing a cylinder and valve mechanism for one piston only.

It` will be recognized that the compressor is well adapted to multiple stage gas compression as well as being advantageous for use in a single sta-ge gas compressor. The control valve. and operating mechanism are of rugged construction yand adapted to a long operation withoutthe necessity of. frequent or accurate adjustment and with uid operation the parts are capable of a long wearing life.

We have, in the drawings and specication presented a -detailed disclosure of the preferred embodiments of our invention, ybut it is to be understood that we do not intend to limit the invention to the specic form disclosed, but intend vto cover all modifications, changes and alternative constructions and methods falling within the scope of the principles taught byl our invention.

We claim. as our invention:

1. A compressor and control system for compressing a gas comprising a compression chamber, a pair of opposed pistons reciprocable in said chamber, smaller gas delivery extension chambers projecting from the ends of the compression chamber, extensions for each of the pistons slidably projecting into said chamber extensions, gas delivery conduits leading from the ends of said chamber extensions, gas delivery passageways leading through the center of each of said pistons and extending into the piston extensions, a gas intake conduit leading into the chamber between said pistons, a non-return valve in said gas con- Cil duit, 'biasing means. positionedbetweenthe lpiston,s. for. spreading., thepisto'ns VVin an'.y intake stroke, .v'vorkingfluid'A conduits leadingto the yendsfofvtlie r'chamber to movefthe pistons lin a delivery stroke, a working Vfluid controlvalve chamber having a port connected to theworking fluid conduits,. a spoolvalve ,within the .valvehamber andj having. passageways therethrough to, communicateV with the working fluid', port andf'directf a sourceV of 'working uid to thejworking fluid conduit ory toventv the .working fluid from the conduit,V a port` in the, compression chamber adapted'to be exposediwhen aiirzst piston is in its full delivery position, a second port inthe compression cham-' ber in communication withV the rst through a valveI operatingy conduit, a third valve ,operating port in the compression chamber, a. 'valve operating passageway, through the second'piston, said valve operating passage-` way through the secondY piston beingaligned vwith the: second and third valve operating ports when thesecond piston isin va fully discharged position, land a secondvalve operating conduit communicatingjbetween the third port and one end of the valve plunger to move' the spool valve to supplypressurized working fluid to the ends of the pistons whereby the spoolV valve is moved only when bothpistons-areat theend'of theirV deliverystroke.

2.l A gascompressor comprisinga compression chamberin which gasis compressed,V a freevfloati'ng working` piston movable in the chamber in an intake `stroke and' a compression stroke and having a compression side andv a working side, gas valve means communicating with the chamberon the compression side of the piston vfor controlling ,theintak'e and* discharge ofgas from the cham-f ber, a fluid'control valve chamber, a working uid conduit connectedto thevalve chamberand to the compression chamber` on the working side of the pistonsaid valve chamber having a first port connected tosaid work'- ing iluid conduit, a second port for connecting to a source ofv pressurized fluid, and, a third open' port for venting fluid, a valve spool slidable in said chamber between la' venting position andy a kiiuid delivery position, said li'rst and vsecondports being in `commur'iica'tion` in said4 de-A livery position,` and,` saidV first andv third ports beingin communication in lsaid venting position, a valve, control port in said compressionchamber positioned to bel uncovered by the piston aty the4 end. of lits intake stroke, means for delivering` pressurized Huid to the control port while it is uncovered by said piston, a. valveoperating line connectedy between said control port and said valve chamber to move the valve spool to said deliveryposition with a ow ofpressurized' iluidfrom said control port, means for moving saidvpiston inv said. intake stroke when the working fluid is vented through said conduit and valve, and means for returning said valve spool to venting position when said control port is covered and the uid ,pressure delivery t'o said valve spool is terminated;

3. Agas compressor comprising a compression chamber in which gasis compressed, a' pair of opposed freely movable pistons in said chamber adapted for movement toward and away from each otherin van intakerand a discharge stroke, gas' valve means Vcommunicating `with said chamber to control the intake and discharge of,` gas from the chambenfiuid valve means communicating withvthe chamber for controlling the intake and discharge of working fluid from the other end ofthe pistons, said fluid moving the pistons in their discharge stroke, means for moving the-pistons vin their intake stroke,. and control means intermittently changing the position of saidl iluid valve means for reciprocating the pistons and compressing the gas as they move in opposing directions in the chamber.

4. A gas compressor comprising a compression charnber in which gas is compressed, a pair of opposed freely movable pistons in said chamber adapted for movement toward and away from each other in an intake and a discharge stroke, gas ports in the chamber for the intake and discharge of gas at one side of each of the pistons, uid ports in the chamber for the intake and discharge of working Huid at one side of each of the pistons, said working uid moving the pistons in their discharge stroke, means for moving the pistons in their intake stroke, gas valve means communicating with said gas ports controlling the intake and discharge from the chamber, iluid valve means communicating with said huid ports controlling the intake and discharge of working fluid from the other end of the pistons, said fluid valve means being fluid operated, and valve operating ports in the Chamber positioned to be covered or opened by movement of the pistons and connected to the liuid valve means whereby movement of the pistons changes the positions of the fluid valve means.

5. A gas compressor comprising a compression chamber in which gas is compressed, a pair of opposed freely movable pistons in said chamber adapted for movement toward and away from each other in an intake and a discharge stroke, gas ports in the chamber for the intake of gas when the pistons move away from each other and for the discharge of gas as they move toward each other, fluid ports at the ends of the chamber to admit and dis charge working fluid to operate the pistons, a spring means positioned to urge the pistons away from each other for moving the pistons apart in their intake stroke and to force working uid out of said ports, gas valve means communicating with the gas ports, uid valve means communicating with the fluid ports, and control means for intermittently changing the position of said fluid valve, means for moving the pistons together to compress gas and permitting the pistons to move in opposing directions to discharge working fluid and draw 1n gas.

6. A gas compressor comprising a compression chamber in which gas is compressed, a pair of opposed freely movable pistons in said chamber adapted for movement toward and away from each other in an intake and a discharge stroke, gas ports in the chamber for the intake and discharge of gas at one side of each of the pistons, fluid ports in the chamber for the intake and discharge of working uid at one side of each of the pistons, said working fluid moving the pistons in their discharge stroke, means for moving the pistons in their intake stroke, gas valve means communicating with said gas ports con trolling the intake and discharge from the chamber, uid valve means communicating with said uid ports convtrolling the intake and discharge of working fluid from the other end of the pistons, and valve positioning means operatively connected to the pistons whereby as the pistons reach one end of their stroke the fluid valve means is changed in position to move the pistons to the other end of their stroke so that the pistons are self actuating.

7. A gas compressor comprising a compression chamber in which gas is compressed, a pair of opposed freely movable pistons in said chamber adapted for movement toward and away from each other in an intake and a discharge stroke, gas ports in the chamber for the intake of gas when the pistons move away from each other and for the discharge of gas as they move toward each other, uid ports at the ends of the chamber to admit and discharge working fluid to operate the pistons, a spring means positioned to move the pistons away from each other for moving the pistons apart in their intake stroke and to force working uid out of said ports, gas valve means communicating with the gas ports for permitting the discharge and intake of gas, and a single fluid valve with conduits communicating with the fluid ports at opposite ends of the chamber to simultaneously admit Working uid to the ends of both pistons.

8. A gas compressor comprising a compression chamber in which gas is compressed, a pair of opposed freely movable pistons in said chamber adapted for movement toward and away from each other in an intake and a discharge stroke, gas ports in the chamber for the intake of gas when the pistons move away from each other and for the discharge of gas as they move toward each other, fluid ports at the ends of the chamber to admit and discharge working uid to operate the pistons, a spring means positioned to move the pistons away from each other for moving the pistons apart in their intake stroke and to force working iiuid out of said ports, gas valve means communicating with the gas ports, a fluid control valve chamber having uid passageways connecting to the tiuid ports in the ends of the chamber, a valve spool movable therein and having iinid passageways to be aligned with the passageways of the valve chamber, and valve operating passageways communicating with the compression chamber to change the position of the valve spool in one stroke of the piston whereby the fluid control valve is actuated by the piston.

9. A gas compressor comprising a compression chamber in which gas is compressed, smaller extension gas delivery chambers at the ends of the chamber, a pair of opposed freely movable pistons in said chamber adapted for movement toward and away from each other in an intake and a discharge stroke, extensions on each of said pistons slidably extending into the extension gas delivery chambers, passageways through each of the pistons communicating between the Space between the pistons and the gas delivery chambers, a spring means positioned to urge the pistons away from each other for moving the pistons apart in their intake stroke and forcing fluid from the spaces between the ends of the chamber and the pistons, and a fluid control valve communicating with the chamber at the ends of the pistons to admit working Huid to the ends of the chamber for simultaneously forcing the pistons together.

l0. A gas compressor comprising a compression chamber in which gas is compressed, a pair of opposed freely movable pistons in said chamber adapted for movement toward and away from each other in an intake and a discharge stroke, gas valve means communicating with said chamber to control the intake and discharge of gas from the chamber, uid valve means communicating with the chamber on the other side of the piston for controlling the intake and discharge of working uid from the other end of the pistons, said working fluid moving the pistons in their discharge stroke, means for moving the pistons in their intake stroke, and a control means connected to the iluid valve means and operated by both of the pistons and operative to terminate the supply of operating fluid only after both pistons have completed their discharge stroke.

References Cited in the file of this patent UNITED STATES PATENTS Brun May l, 1934 

